You used scale factors to solve problems with
similar polygons.
• Interpret scale models.
• Use scale factors to solve problems.
Vocabulary
Scale model/scale drawing – an object or drawing with
lengths proportional to the object it represents.
The scale of a model or drawing is the ratio of a length
on the model or drawing to the actual length of the
object being modeled or drawn.
The scale on a map relates the size of an object on
the map to its actual size.
Where do you find the scale on a map?
Use the scale and algebra to find the distance
between Mishawaka and Kokomo.
MAPS The distance between Boston and Chicago on a
map is 9 inches. If the scale of the map is
1 inch: 95 miles, what is the actual distance from Boston
to Chicago?
Method 1 Write and solve a proportion. Let x
represent the distance between Boston and Chicago.
1 ● x = 95 ● 9
x = 855 miles
Cross Products Property
Simplify.
Method 2 Write and solve an equation.
Let a = actual distance in miles between Boston and
Chicago and m = map distance in inches. Write the scale
as
, which is 95 miles per inch. So for every inch on
the map, the actual distance is 95 miles.
a = 95 ● m
= 95 ● 9
Write an equation.
m=9
= 855
Solve.
Answer: The distance between Boston and Chicago is
855 miles.
Check
Use dimensional analysis.

MAPS The distance between Cheyenne, WY, and Tulsa, OK,
on a map is 8 inches. If the scale of the map is 1 inch : 90
miles, what is the actual distance from Cheyenne to Tulsa?
A. 800 miles
B. 900 miles
C. 630 miles
D. 720 miles
Using Scale Factors
The scale factor of a drawing or scale model is written
as a unit-less ratio in simplest form. Scale factors are
always written so that the model length in the ratio
comes first.
A. SCALE MODEL A miniature replica of a fighter jet is 4
inches long. The actual length of the jet is
12.8 yards. What is the scale of the model?
To find the scale, write the ratio of a replica length to an
actual length.
Answer:
The scale of the model is
1 in. : 3.2 yd.
B. SCALE MODEL A miniature replica of a fighter jet is 4 inches
long. The actual length of the jet is
12.8 yards. How many times as long as the actual is the model jet?
To answer this question, find the scale factor of the
model. Multiply by a conversion factor that relates
inches to yards to obtain a unitless ratio.
Answer:
The scale factor is 115.2 : 1. That is, the actual jet is
115.2 times as long as the model.
A. SCALE MODEL A miniature replica of a fire engine is 9
inches long. The actual length of the fire engine is 13.5
yards. What is the scale of the replica?
A. 2 in. : 3 yd
B. 1 in. : 3 yd
C. 2 in. : 5 yd
D. 3 in. : 4 yd
B. SCALE MODEL A miniature replica of a fire engine is 9
inches long. The actual length of the fire engine is 13.5
yards. How many times as long as the model is the actual
fire engine?
A. 48
B. 54
C. 60
D. 63
SCALE DRAWING Gerrard is making a scale model of his classroom
on an 11-by-17 inch sheet of paper. If the classroom is 20 feet by
32 feet, choose an appropriate scale for the drawing and
determine the drawing’s dimensions.
The actual classroom is 20 feet wide.
20 feet ÷ 11 inches = 1.8 feet per inch
The actual classroom is 32 feet long.
32 feet ÷ 17 inches = 1.8 feet per inch
A scale of 1 inch = 2 feet would be appropriate.
So, for every inch on the paper p, let the actual measure a be 2 feet.
Write this as an equation.
length:
width:
a = 2 ● p Write an equation.
a = 2 ● p Write an equation.
20 = 2 ● p a = 20
32 = 2 ● p a = 32
16 = p
Divide each side by 2.
10 = p Divide each side by 2.
Answer: 1 in. : 2 ft; 10 in. wide, 16 in. long
ARCHITECTURE Alaina is an architect making a scale model
of a house in a 15-by-26 inch display. If the house is 84 feet
by 144 feet, what would be the dimensions of the model
using a scale of
1 in. : 6 ft?
A. 14 in. × 24 in.
B. 14 in. × 25 in.
C. 15 in. × 25 in.
D. 15 in. × 26 in.
7-7 Assignment
Page 520, 5-12